In continuous tone and halftone reproduction or enlargements, it is hardly ever possible to reproduce the entire tonal range of the copy on the printed sheet. Even high speed emulsions or the combination of such emulsions with a halftone screen which records a long density range cannot prevent the loss of some of the tones of the original. It is common practice to overcome these difficulties by giving an "auxiliary exposure". Process cameras and enlargers are equipped with so-called "auxiliary exposure devices" which can be tilted in front of the lens (on the side of the original).
This kind of exposure has the disadvantage that it flattens the overall contrast of the image. While it affects the highlights and bright areas of the image very little, the effect becomes more and more pronounced with a density increase in the shadow area. The result is a loss of detail in the shadows and a grey appearance of the 75 percent tones.
It must therefore be the aim of a satisfactory reproduction to confine the flattening effect of the exposure to the middle tones and to leave the contrast in the highlights and shadows unaffected. In color work, this aim is reached by making one or several color correction masks prior to the color separation. The mask negatives have an S-shaped characteristic curve. Highlights and shadows of the mask are flat so that the copy contrast in these areas remains materially unaffected. The steeper slope of the characteristic curve in the middle tones decreases the copy contrast in these areas.
Masking methods are generally applied in color work. They would, however, be much too expensive and too time-consuming for improving black and white reproductions.
It is therefore the purpose of this invention to propose a process and means for improving the quality of both black and white and color work by recording a satisfactory tonal scale without the use of masking methods. A "satisfactory" tone scale records the full contrast of the highlight and shadow areas of the copy, while the contrast of the brighter and darker middle tones is decreased, the amount of decrease depending on the limitations inherent in the printing process applied.
The gist of this invention lies in a method and an apparatus for projecting one and the same copy, for instance color transparency, onto one and the same imaging plane where they are both photographically recorded, either simultaneously or consecutively, in black and white or in color. Two different transmission systems are used for this operation; viz., a first process lens on a first optical axis for direct recording of the main image therefrom, on the one hand, and a short focal length lens of a black and white television camera on a second optical axis for recording a negative secondary image thereon, on the other hand. After going from the television camera lens through a photo-cathode in the television camera, the secondary image is sent through an amplifier and a negative-converter to a plane telescreen located in the picture tube of a video-monitor having optoelectronic contrast and brightness control and on through a second process lens for projecting and superimposing said negative secondary image on the main positive image thereof.